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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 17th Feb 2020, 3:27 pm   #1
Strange Brew
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Default Replacement bulbs with LED question

I have been given a lovely little PPM unit and I've got a a question which someone may be able to answer for me.

Firstly the light bulbs for the illuminated display have blown.

To what I can see the bulbs are rated at 6.5v 300mv. There are 4 bulbs all together, all of which have blown.

Would you be able to advise me to which LED bulbs would work in it?

Many thanks
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Old 17th Feb 2020, 3:48 pm   #2
toshiba tony
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Default Re: Replacement bulbs with LED question

Sorry, just a minor point, it's ma. For dial lights that sounds a tad high though

And sorry, whats a ppm, probably the right name, it's me a bit lacking.
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Old 17th Feb 2020, 3:59 pm   #3
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Default Re: Replacement bulbs with LED question

Probably in the wrong section-not a vintage radio at all.Les
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Old 17th Feb 2020, 3:59 pm   #4
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Default Re: Replacement bulbs with LED question

Hi.

It's a peak meter, like a VU meter.

Sorry, yes, it's mA.
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Old 17th Feb 2020, 4:00 pm   #5
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Default Re: Replacement bulbs with LED question

Quote:
Originally Posted by TowerRadio View Post
Probably in the wrong section-not a vintage radio at all.Les
Oh, sorry... well, it's used with my radio. LOL Hope that's okay.
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Old 17th Feb 2020, 4:13 pm   #6
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Default Re: Replacement bulbs with LED question

If they're MES screw fit bulbs why not just replace them? Would be a lot more authentic than an LED conversion. Spiratronics sell a pack of 5 for £2.90 inc postage.

Alan
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Old 17th Feb 2020, 4:20 pm   #7
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Default Re: Replacement bulbs with LED question

Four bulbs does seem an awful lot of light for a panel meter and presumably generate a relatively large amount of heat so changing to LEDs make sense.

LEDs radiate illumination basically in one direction, whereas a incandesent filament radiates in all directions. Replacing a bulb with a LED is not always straightforward and you will need to work out how the light from a LED is going to end up where it meant to be.

Ian


If this 'ppm unit' has a moving coil meter
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Old 17th Feb 2020, 4:24 pm   #8
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Default Re: Replacement bulbs with LED question

Thanks... so long as the LED fires forward at the very least then that would be fine.

I can't seem to find a direct drop in LED replacement.
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Old 17th Feb 2020, 5:40 pm   #9
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Default Re: Replacement bulbs with LED question

https://www.ebay.co.uk/itm/4pcs-E10-...MAAOSw~p5crDgv

Should be close enough at 6V but perhaps I'm missing something.

Alan
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Old 17th Feb 2020, 6:15 pm   #10
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Default Re: Replacement bulbs with LED question

sometimes dial lights are wired in series, or sometimes from a higher voltage than required with a dropper resistor on the board. I would make sure of how everything is supplied before just shoving LEDs in.

As an example there is an old audio amp I'm familiar with that uses 2 bulbs per VU meter and another in the power switch. They are all series connected across the DC bus with a shunt resistor across the power switch (which uses a smaller bulb) and a series resistor across the whole chain.

Maybe I'm muddying the waters but forewarned is forearmed
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Old 17th Feb 2020, 6:15 pm   #11
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Default Re: Replacement bulbs with LED question

If this is AC LEDs will flicker annoyingly. Get real bulbs, maybe 6V 60mA types, available from all good bicycle shops and run cooler than 300mA ones. Should be enough light.
 
Old 17th Feb 2020, 6:17 pm   #12
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Default Re: Replacement bulbs with LED question

Valid point Kevin, I would suggest the OP checks each bulb, at least with a filament type you can see if the filament is intact.
 
Old 17th Feb 2020, 7:05 pm   #13
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Default Re: Replacement bulbs with LED question

Quote:
Originally Posted by McMurdo View Post
sometimes dial lights are wired in series, or sometimes from a higher voltage than required with a dropper resistor on the board. I would make sure of how everything is supplied before just shoving LEDs in.

As an example there is an old audio amp I'm familiar with that uses 2 bulbs per VU meter and another in the power switch. They are all series connected across the DC bus with a shunt resistor across the power switch (which uses a smaller bulb) and a series resistor across the whole chain.

Maybe I'm muddying the waters but forewarned is forearmed
I think you might be on to something.

I've attached a picture. Hope you can see it.
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Old 17th Feb 2020, 7:58 pm   #14
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Default Re: Replacement bulbs with LED question

They are in series, is there (as suggested by McMurdo) a series resistor too? A picture of where the wires go to will help.
 
Old 17th Feb 2020, 8:39 pm   #15
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Default Re: Replacement bulbs with LED question

Have we confirmed that they are MES bases? It's not obvious that they are from the picture.
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Old 17th Feb 2020, 9:00 pm   #16
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Default Re: Replacement bulbs with LED question

Some more pics for you.
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Old 17th Feb 2020, 9:01 pm   #17
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Default Re: Replacement bulbs with LED question

Oh.. and I found these too.

I emailed the company and they suggested they might work

https://internationallamps.co.uk/pro...e10-mes-white/
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Old 17th Feb 2020, 9:17 pm   #18
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Default Re: Replacement bulbs with LED question

Given the size of the unit, it'll hardly run hot as is. If they're too bright, add a series resistor in the chain. 22 ohm 2.5W would do nicely. The bulbs will probably last for ever too being underrun by about 20%.
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Old 17th Feb 2020, 10:19 pm   #19
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Default Re: Replacement bulbs with LED question

There's something not quite right about all of this. The bulbs look like they're connected to an output of the PSU rated at 18V and .28A. Four series connected bulbs marked 6.3V at .3A each doesn't make much sense unless I'm completely misinterpreting the arrangement. As the unit has an unknown history I'm wondering whether or not someone's previously fitted the wrong bulbs. Does it otherwise work correctly? I know the bulbs don't work but have you tested each of them for continuity or can you see that the filaments have broken?

Alan
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Old 17th Feb 2020, 10:50 pm   #20
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Default Re: Replacement bulbs with LED question

Knowing the make and model would help too as someone might be able to track down a circuit diagram.

Alan
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